The present invention relates to a pedal force sensing apparatus for an electric bicycle, especially to an apparatus capable of sensing the pedal force of an electrical bicycle for driving an electrical motor to output an adequate auxiliary force during biking.
The power transmission mechanism of a conventional electric bicycle generally comprises a high-speed electric motor as an auxiliary power source to help a cyclist overcome a road rough for biking. A gear reduction mechanism reduces the output speed of the motor so as to accordingly increase the output torque. The power from the motor after speed reduction and the pedaling power from the cyclist are coupled together by a power combining mechanism, and subsequently are transmitted to a chain wheel for driving the electric bicycle forward at a labor-saving mode.
In order to accommodate the output power of the motor to a road of variable conditions, a pedal force sensing apparatus is provided on a pedal transmission path to detect the magnitude of the pedal force to thereby adjust the output force of the motor for saving the applied force from cyclist.
Conventional electric bicycles with pedal force sensing function are categorized into two types. In one of the types, the electric bicycle is simply controlled by a switch. When the pedal force is larger or smaller than a threshold value, the power of the motor is turned on or turned off by the switch. In the other type, a pedal force sensing apparatus can detect the magnitude of the pedal force, and the output power of the motor is depended on the sensed pedal force. If the output power of the motor is only controlled by the switch, there is not a flexible auxiliary force to satisfy the bicyclist. On the other hand, the conventional pedal force sensing apparatus generally employs a set of complicated planetary bevel gears to have a different action, and a relative angular displacement occurred in the different action is transferred to a sensed pedal force. Regarding the aforesaid pedal force sensing apparatus, several advanced companies worldwide, e.g., Japanese YAMAHA Co. and Japanese HONDA Co., currently provide an electric bicycle with this function. However, the electric bicycle has a high cost and a quite complicated mechanism including a great deal of transmission parts.
In summary, it is an important issue for the electric bicycle industry regarding how to provide a pedal force sensing apparatus with an uncomplicated structure so as to reduce the manufacturing cost of the electric bicycle.